Instruments
The 4 TPB constructs (attitude, subjective norm,
PBC, and intention not to use illicit drugs) were
measured by questions designed according to the TPB
manual for constructing questionnaires.18 Life skills
were measured by questionnaires designed by our
research team.
Before data collection, the questionnaires were
reviewed by 5 experts, including 2 senior health
education teachers, 2 professors of health education,
and a section director of the Division of Controlled
Drugs, Food, and Drug Administration (FDA), Taiwan.
The content validity index (CVI) was applied to
evaluate whether items were relevant and appropriate
in measuring study constructs. Questionnaire CVI
was .95. A CVI larger than .80 is considered
acceptable.19 The questionnaire was evaluated by a
focus group that modified questions to make it more
readable, understandable, and culturally suitable for
students.